As is known, a motor-vehicle assembly line normally comprises a plurality of workstations aligned to, and set at a distance from, one another, a fixed conveying guide, which extends through the workstations in a given direction of advance, and a plurality of conveying units, each of which is designed to support a respective body and is mounted so as to slide along the conveying guide for displacing, with continuous or steplike motion, the body itself through the workstations.
In general, a conveying unit of a known type is defined by a gondola, which is suspended from a slide slidably coupled to the fixed guide and comprises an arched element designed to embrace laterally the body, and a supporting element, which is set at the free ends of the arched element and is designed so that it couples to the bottom panel of the body itself.
The suspension of the gondola from the slide is made in such a way as to enable the gondola to oscillate, with respect to the fixed guide, about an axis of its own parallel to the aforesaid direction of advance and to rotate the body between a normal plane position, where the bottom panel faces downwards and is substantially parallel to the floor, and a position rotated upwards, where the bottom panel is inclined, with respect to the floor, by a sufficiently wide angle, normally between 45° and 90° so as to enable operators to carry out work on the underbody conveniently.
To perform rotation of the gondola in given stages of the assembly process, it is known to provide, in the corresponding stretches of the assembly line, fixed deviator elements, each of which is shaped in such a way as to couple in succession to the arched elements and rotate each arched element by a respective pre-set angle. Each conveying unit is moreover provided with a blocking device designed to keep the respective arched element in the inclined position.
A solution of this type is known, for example, from JP 52002971 and JP 52043277. In particular, JP 52043277 discloses an arched hanger arm rotatably inserted between the two pairs of rotatable guide rollers which are rotatably supported by a suspension mechanism of an hanger body which is driven by a overhead conveyer 2. The hanger arm is provided on its outer peripheral edge with a chain extending therealong and is rotated by a rotation mechanism having a gear which engages with the chain. The rotation mechanism comprises a gear set mounted on the hanger body and comprising a first bevel gear coaxial to the gear which engages with the chain, a second bevel gear which engages with the first bevel gear, a spur gear coaxial to the second bevel gear, a rack which engages with the spur gear in parallel with the overhead conveyer and which is arranged so as to rotate the hanger arm, and a reversing rack which engages with the spur gear to thereby reverse the hanger arm. Thus, the hanger arm is rotated or returned in by the movement of the hanger body.
Even though widely used on account of its simplicity, such a solution suffers, however, from certain drawbacks that can be put down principally both to the fact that the deviator elements have relatively large overall dimensions, which obviously complicates the structure of the assembly line, and to the fact that the deviator elements, being fixed, do not enable substantial modifications of the assembly process, for example modification of the stages of the process in which the bodies must be rotated, without considerable interventions of reconfiguration of the assembly line.
A further drawback derives from the fact that the fixed deviator elements, being “passive” elements, are able to perform rotation of the arched elements only when the respective conveying units displace, engaging with the deviator elements themselves, and consequently prove barely usable in the cases where the assembly line does not advance with continuous motion.
To overcome the above drawbacks, a different solution has been proposed, which envisages providing “on board” each conveying unit an electric actuator capable of rotating the respective arched element independently in pre-set workstations.
An example of this solution is provided by the document No. U.S. Pat. No. 5,234,096.
Albeit effective, said solution presents the drawback of proving considerably burdensome both from the standpoint of its construction and from the economic standpoint.